Unexplained charges

I honestly do no understand the “sudden” FNB charges...on saturday I made 2 transactions from my account and then seeing that there was still money left in my account I transferred the balance to my Tymebank account, to my surprise this morning I get a “Pos unpaid” transaction on my account ???????????? how is that even possible when I had more than enough on my account?? Is this how the bank makes money from us? By charging us and hoping we don’t query these transactions?? And secondly...I’m on the premier banking package which is R199 a month but it’s never R199 and I’ve queried this before but never received an answer